Abstract: A hydraulic circuit for a working machine is provided which prevents a decrease in the working speed of a clamshell bucket upon expansion of an expansion arm, so that improvement of the operability can be achieved. A hydraulic circuit for a working machine is configured such that a clamshell bucket is attached to a tip end of an expansion arm and the expansion arm and the clamshell bucket are operated by pressure oil supplied from a common pressure source. The operating pressure is reduced for driving the expansion arm to the expansion side based on the operating pressure for opening the clamshell bucket. By the configuration, the clamshell bucket can be opened rapidly, and improvement of the operability is achieved.

Abstract: A device for controlling a working arm of a working machine, which is capable of releasing the pressure of the actuation fluid confined in the actuation cylinder of the working arm device at a predetermined pressure lower than the set pressure and of controlling the opening/closing of the cylinder relief valve. The device comprises releasing means for a releasing a pressurized fluid feed/drain circuit of an actuation cylinder of a working arm device at a predetermined pressure lower than a set pressure of a cylinder relief valve provided for said feed/drain circuit and a control means for controlling the opening/closing of the releasing means.

Abstract: A carrier vehicle having a swing table supported on an under-carriage so as to swing a full turn, and a planetary reduction gear for reducing the revolution of a drive motor and transmitting it to the swing table. The planetary reduction gear is mounted on the under-carriage under the swing table.